1. Field of the Invention
This invention relates, generally, to speed reducers. More particularly, it relates to a method for making speed reducers from solid metallic blocks by CNC machining.
2. Description of the Prior Art
The conventional way to make a speed reducer is to cast the individual parts thereof in a mold. The parts that are individually cast include the housing and the gears or other power transmission means within the housing. The working parts of the speed reducer are assembled and the completed assembly is placed into the housing.
The housing is typically a box-like structure that encloses the gear train or other power transmission system. The housing not only protects the parts therewithin from the elements, it also acts as a safety cover to protect individuals from sprocket gears, sprocket chains, and the like that may form a part of the speed reducer.
Worms and worm gears are well-suited for use in speed reducers, but there are many other types of gears that can be used. For example, helical, bevel, mitre, and spur gears or any combination thereof can be used.
Nor are gears the only suitable means for performing lifting functions. For example, there are numerous hydraulic, pneumatic, and other power transmission systems that can be employed. However, in most applications a gear train is less expensive and usually more practical than such alternatives.
Speed reducers of the type that employ worms and worm gears have distinct advantages over other gear train power transmission systems. They have particular utility where a high-ratio speed reduction is required but where space is limited. They operate quieter and smoother than speed reducers employing sprocket gears and sprocket chains, helical gear trains, and the like.
Speed reducers that incorporate worms and worm gears also offer good resistance to back driving because a worm gear cannot drive its associated worm. When properly designed and installed for a particular application, they are generally self-locking when the load is at rest. For example, where a boat is lifted from water by a lift that incorporates a worm and worm gear speed reducer, the worm and worm gear speed reducer will self-lock and thus prevent the boat from re-entering the water. When a boat is being lowered, any tendency for lowering to continue after the motor has been turned off is called “inertia-generated coasting.” Worm and worm gear speed reducers are resistant to such inertia-generated coasting.
A worm and worm gear double speed reduction system is even more resistant to inertia-generating coasting, making such systems preferable to other gear systems when used for lifting and lowering heavy loads.
For example, spur gears exhibit little or no resistance to inertia-generated coasting and thus are not suitable for use in applications requiring the lifting of heavy objects where inertia-generated coasting is undesirable.
The success of a design is determined in large part by the gear material selected. For example, a system having steel worms and cast iron worm gears has only half the lifting capacity as a system having hardened steel worms and bronze worm gears.
The designer must also consider the amount of motion between the worm and the worm gear, also known as gear lash, and the lateral motion of the worm, also known as end play.
Moreover, appropriate thrust bearings and lubrication are critical to minimize unwanted friction to ensure efficient operation.
A weight-lifting and holding system is said to have a service factor of 1.0 if the system is subjected to a moderate shock lasting no more than fifteen (15) minutes for each two (2) hour period of uniform operation over a ten (10) hour or less day. A service factor of 1.0 or less is considered normal for the boatlift industry. It follows that a successful design should employ a worm and worm gear speed reducer having a hardened steel worm and a bronze worm gear, should minimize gear lash and end play, and should be installable in small spaces. Ideally, the design should enable the speed reducer to be re-configured as needed so that it can fit into differing areas having limited space.
An ideal design should also maintain the designed gear lash and end play with consistent repeatability, i.e., the gear lash and end play should remain about the same over many cycles of operation.
The known methods for making speed reducers, including the casting of individual parts as mentioned above, assembling the parts, and housing the assembled parts, is a relatively expensive process. If a new method could be found that substantially reduces the cost of manufacturing a speed reducer, it would revolutionize the industry.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the art of making a speed reducer could be advanced in a pioneering way.